The present invention relates to novel nitrile-containing aromatic polyester, polyamide and silicone polymers, and polymers and fibers prepared therefrom. The invention also relates to the preparation of thermally stable fiber-reinforced composites prepared from a mixture of nitrile-containing aromatic polyester, polyamide or silicone fibers and nitrile-containing aromatic polymers, such as silicone, polyester or polyamide polymers, heat treated under pressure in the presence of a catalyst. Copolymers of styrene wherein the phenyl group contains nitrile substituents also are described.
In the ordinary fiber-reinforced resin composites, there usually are only intermolecular adhesion and hydrogen bonding forces between the fiber and the resin. Examples of such fiber reinforced resins include conventional polyester resins reinforced with glass fibers. The absence of mainly chemical bonds between the fiber and the resin limits the strength of the composite. Ideally, the fiber in fiber-reinforced composites should be itself thermally stable if the thermal stability of the composite is a desirable objective. Thus, fibers such as prepared from Nylon 66 and Dacron may be utilized in fiber-reinforced resin composites but said composite is not especially high temperature stable. Other commercially available organic polymer fibers such as Nomax and Kevlar exhibit heat resistance but are not apparently capable of forming chemical bonds between the fiber and the resin.
Recently, high temperature and flame resistant aromatic copolyamide fibers have been described in the text entitled High Temperature and Flame-Resistant Fibers, Applied Polymer Symposia, No. 21, Interscience Publication, John Wiley & Sons, New York, 1972. One group of high temperature aromatic copolyamide fibers disclosed therein contain pendent carboxyl groups. When such carboxyl-containing fibers are used to fabricate composites, chemical bonds between the fibers and resins may exist but gaseous by-products will be produced. The voids in the composites formed on release of the gaseous by-product reduces the strength of the composite.